Post-shot xG and goalkeeper shot-stopping explained
What post-shot xG measures, how it differs from ordinary xG, how it is used to judge a goalkeeper's shot-stopping, and how to read it sensibly.
The idea in one sentence
Post-shot expected goals, often shortened to PSxG, measures the quality of a shot after it has been struck, based on where it is heading. It only counts shots on target, and it takes into account how well the shot was placed, so a fierce effort into the top corner is rated far more likely to score than a tame one straight at the goalkeeper. It is a way of valuing not the chance, but the finish.
How it differs from xG
Ordinary expected goals rates a chance at the moment it is created, before the shot is taken, using factors like distance and angle. Post-shot xG waits until the ball has left the boot and adds the crucial extra information of placement. A weak shot from a good position has high xG but low PSxG, while a perfectly placed strike has a high PSxG. One judges the opportunity, the other judges how dangerous the shot actually was.
Judging a goalkeeper
Post-shot xG is most useful for evaluating goalkeepers, because it estimates how likely each shot on target was to beat a keeper. Adding up the PSxG of all the shots a goalkeeper faces gives the number of goals an average keeper would be expected to concede. Comparing that with the goals actually conceded reveals shot-stopping quality: a keeper who lets in fewer than expected is preventing goals, one who lets in more is costing them.
How to read it sensibly
The gap between PSxG faced and goals conceded is often called goals prevented, but it needs care. It is a shot-stopping measure only and says nothing about a keeper's positioning, command of the area or distribution, all of which matter. It is also noisy over a handful of games and best judged across a season. And it can be shaped by the defence, since a keeper who faces mostly weak, well-defended shots will flatter the numbers.
Where you will see it
Post-shot xG appears throughout goalkeeper analysis and recruitment, usually presented as goals prevented over a season. It has become the standard way of separating a keeper's shot-stopping from the quality of the defence in front of them. Read alongside more traditional judgements of a keeper's all-round game, it offers one of the clearest available measures of how well a goalkeeper does the core job of keeping shots out.